There’s a surplus of gamma rays spewing forth from the center of our galaxy, and astrophysicists say they don’t know where it’s coming from. One thing is clear, though: it could not have been caused by anything we consider ordinary in our galaxy.

What it could be, according to Tracy Slatyer of MIT and her colleagues at Fermilab, Harvard, and MIT, is excess light from colliding dark matter particles. If true, this observation would be the first-ever indirect detection of dark matter in our universe.

This map shows an excess amount of gamma rays coming from the center of the Milky Way, possibly indicating the presence of dark matter.

Physicists believe that dark matter is made of weakly interacting massive particles (WIMPs), which act simultaneously as matter and anti-matter, annihilating each other when they meet. That collision gives birth to normal matter in the form of high-energy photons of gamma-ray light. Currently, we have some of our best eyes, including the Fermi space telescope, pointed toward the Milky Way’s center—where dark matter should be the densest—to search for the results of these collisions. In sifting through data collected but the Fermi telescope, Slatyer and her colleagues found about 10,000 extra photons in the 5,000-light-year space surrounding the center of the galaxy. It was an unexpected result.

One possibility is that dark matter may be interacting via a new type of intermediary particle besides the Z or Higgs bosons, associated with an unknown fifth fundamental force. “It would be very exciting if through discovering dark matter, we also discovered a new force of nature,” Slatyer says.

What scientists are seeing might not be the results of dark matter-dark matter collisions, after all—it could just be a new, previously unknown class of pulsar, for example. To know for sure, astrophysicists want to look at neighboring galaxies that are expectedly dark matter-rich in their centers. If the same excess of gamma-ray light occurs there, too, they could be onto something.